Dark beak disease in baby chickens

Hello, I need some urgent help please. Our baby chickens are dying due to some strange disease, the beak turns black and then they die. Only 3 left now from the initial 9 chickens... Anyone has any idea of what cause and treatment? Thank you

I've never heard of this, and did a bit of research, but nothing came up. Must be pretty rare to have stayed unreported. Sorry if this isn't much help, but I'd suggest you clean and bleach the brooder, change bedding, give them about a teaspoon of apple cider vinegar per quart of water, and report the incident to the hatchery or breeder you got them from. :/